Portable computing devices such as tablet personal computers (hereinafter referred to as “tablet PCs), smartphones, personal digital assistances (PDAs), and electronic book readers are becoming more ubiquitous. Many portable information devices use a touch panel together with a display device. Such devices often use software keyboards, also known as on-screen keyboards (OSKs) or screen keyboards, to obtain input from the user through the touch panel.
However, unlike physical keyboards, wherein the key must be physically depressed to trigger a key input, software keyboards appear on a flat display and a key input can be performed by mere contact of a finger with a touch panel without the movement of a physical key. Thus, if a finger remains on the software keyboard, it is difficult for a portable information device to determine whether the presence of the finger is intended to be a key input or not.